The silicon condenser microphone is typically comprised of two basic elements which are a sensing element and a pre-amplifier IC device. The sensing element is basically a variable capacitor constructed with a movable compliant diaphragm, a rigid and fixed perforated backplate, and a dielectric spacer to form an air gap between the diaphragm and backplate. The pre-amplifier IC device is basically configured with a voltage bias source (including a bias resistor) and a source follower preamplifier. Although there have been numerous embodiments of the variable capacitor on silicon substrates, each prior art reference included in related patent application Ser. No. 10/977,692 has a dedicated backplate in the construction of the microphone sensing element.
The inclusion of a dedicated backplate in the microphone sensing element normally leads to manufacturing complications due to its special definitions in material and processing method. The required photolithographic masking levels as well as the processing issues relating to overlay and spacing between the diaphragm and backplate normally result in a complex and high cost fabrication.
Therefore, a simply defined silicon microphone structure is needed that enables the fabrication process to be simplified at a reduced cost. In particular, a novel design for the variable capacitor component is desirable so that fewer masking levels are needed to produce a microphone sensing element. Advanced designs are needed to accommodate various shapes and features in a silicon microphone device that will provide more flexibility in terms of movable parts and thereby lead to better reliability. An advanced design in which a silicon microphone structure can be integrated with a CMOS device would be especially advantageous.
An improved design with regard to better impact reliability has been disclosed in related patent application Ser. No. 11/973,075 which includes a means for using bonding wires to constrain the vibration of the diaphragm in a direction away from the substrate.